The present invention relates to a method for manufacturing an intake manifold, which forms a part of an intake system of an automobile engine, and an intake manifold.
Conventionally, the structure of an intake manifold shown in FIG. 4 is known. The conventional structure is for a horizontally opposed engine. In this conventional structure, an intake manifold 41 is entirely made of a heat-resistant plastic and includes a central surge tank 42 and intake pipes 43 extending in curved shapes from opposite sides of the surge tank 42. The surge tank 42 and the intake pipes 43 of the intake manifold 41 are formed by a main portion 411 having an upper opening and a cap portion 412 closing the opening of the main portion 411. The main portion 411 and the cap portion 412 are both formed of plastic, and the cap portion 412 is fixed to the opening of the main portion 411, for example, by vibration welding, so that the intake manifold 41, which has the surge tank 42 and the intake pipes 43, is formed.
Another example of conventional intake manifolds is disclosed in Japanese Laid-Open Patent Publication No. 62-99665. In this conventional structure, the distal ends of intake pipes are attached to the main body of an engine via an intake passage block. The intake pipes and the intake passage block have connection flanges at the facing ends. With a gasket arranged between the connection flanges, each intake pipe and the intake passage block are connected and fixed to each other with bolts.
The intake manifolds of the above described conventional configurations have the following drawbacks. In the conventional configuration of FIG. 4, since the intake manifold 41 is entirely formed of plastic, and the intake pipes 43 extend in a curved manner from both sides of the surge tank 42, the ends of the intake pipes 43 are likely to be warped upward or deformed during molding. That is, in some cases, warping W as shown in FIG. 5 is caused at distal attachment surfaces 431 of the intake pipes 43 on the opposite sides. In other cases, as shown in FIG. 6, the measurement L1 between the intake pipes 43 on the opposite sides deviates from a specified measurement L2. Further, as shown in FIG. 7, a height difference S is caused between the distal attachment surfaces 431 of the intake pipes 43 on the opposite sides in other cases. The longer the intake pipes 43 on the opposite sides of the surge tank 42, the more likely such warping and deformation are to occur. Further, in the case in which the surge tank 42 and the intake pipes 43 of the intake manifold 41 are formed by the main portion 411 and the cap portion 412, warping and deformation are even more likely to occur because of the upper opening of the main portion 411 during molding of the main portion 411.
To reduce warping and deformation occurring in the intake pipes 43 during molding, ribs may be formed on the outer surface of a part of each intake pipe that is located in a position to be extended by warping. However, if the intake pipes 43 have such ribs, the shape of the molding die would be complicated. Further, the molded intake manifold would have a complicated structure, and the ribs would create fins. The fins become relatively thick in some cases so that sink marks are formed due to thickness differences.
The conventional configuration disclosed in Japanese Laid-Open Patent Publication No. 62-99665 is a structure in which an intake passage block is connected to the distal ends of intake pipes of an intake manifold for a horizontally opposed engine. However, the document has no disclosure regarding the type of the material used for the intake manifold. Accordingly, drawbacks caused by the material of the intake manifold are not disclosed.
The present invention was made for solving the above problems in the prior art. It is an objective of the present invention to provide a method for manufacturing a plastic intake manifold and an intake manifold that, when distal members are secured to the distal ends of intake pipes, limit adverse influence of warping and deformation of intake pipes caused during molding.